This warlock shares the exact same appearance as the boss Prowling Magus.
The Aldia Warlock will start attacking you from a far range, although telegraphs its attacks slowly, making it very easy to dodge or strafe attacks. This enemy wears little armor and deals less than impressive damage and so is easy to stagger and stunlock with a two handed light weapon. Players also need to be careful on one specific attack, Because this enemy is located on a cliffside the dark Force attack can cause you to fall off the edge.
This is the ONLY Non-Phantom enemy that that will drop the Warlock Mask and Cursed Bone Shield (Before and after NG+). This makes these items very rare as this enemy does not respawn without the aid of a Bonfire Ascetic. It is Recommended to farm these items on this enemy (As opposed to Red Invader Merciless Roenna, who is also an Aldia Warlock variant) as bonfire ascetics only effects this enemy and a few Hollowed Milfanitos.
Generally, they wear Warlock Mask, Lion Mage Cuffs, Priestess Robe and Skirt (can be identified by Merciless Roenna), the incantation is same as Whisper of Despair, and they're also Fenito, this can be indentified by their cyan skin tone and crimson eyes, as shared with the other Grave Wardens. The catalyst/halberd (not to be confused with Roaring Halberd; this one is double-edged) they wield shares the same design as the one wielded by one of the three Skeleton Lords, although you cannot obtain the catalyst by any means.
It is speculated the Warlocks were once Drangleic Priestesses, which can be identified by the robe, as with the location of the Prowling Magus: the church, but they've sided with Lord Aldia, turned themselves into Fenito, a race of the guardians of the dead, acted as a false idol, lured many Undead Citizen and even Milfanito into Aldia's Keep or Sinners' Rise, and converted them into Undead Aberrations in order to recreate the extincted Dragon.
Another theory is Fenito are probably a species created by Lord Aldia rather than being naturally existed, and that Aldia Warlocks acted as a successor among all the Fenito of Aldia's creations if compared to Navlaan, Najka, and Tark.
Oddly, they were supposed to appear in King's Passage (via the TGS Trailer), but were moved to Shrine of Amana.